This invention relates to an improved toner cartridge for use in a laser printer and, more particularly, to a toner cartridge for use in a laser printer utilizing an arrangement for improving print quality and print speed.
Print quality in a laser printer is improved when the size of the toner particles is reduced. This size reduction of the particles allows more of the particles to print in a specific area so that there is more overlapping of the particles during development of an image on a medium such as paper, for example.
It also is desired to increase print speed. This results in the need for a lower melt point toner so that the toner will fuse faster on the medium.
Lower melt point toners are more prone to clumping to make it more difficult to convey the toner from its supply hopper or reservoir to the image development zone of the laser printer. This is because lower melt point toners have inherently lower flow rates than previously employed toners with higher melt point temperatures.
Inadequate conveyance of the lower melt point toner due to its lower flow rates can lead to insufficient toner in the image development zone; this reduces print quality even though the size of the toner particles has been decreased to improve the print quality. This insufficient toner in the development zone is referred to as xe2x80x9ctoner starvation.xe2x80x9d
Various mechanical arrangements have been employed to aid in conveyance of the toner. These include rotating rods, reciprocating rakes, gravity assisted inclines, and a pivotally mounted agitator, for example.
U.S. Pat. No. 5,875,378 to Campbell et al discloses an agitator pivotally mounted about its end points and located in a transition opening between the supply hopper and the image development zone. The agitator is driven upwardly by a rotating paddle, which passes through the toner in the supply hopper, to a point at which their curved paths separate. Then, the agitator falls by gravity until it returns to its home or rest position, which is proximate to an exit surface sloping downwardly during normal operation of the toner cartridge.
Falling of the agitator by gravity displaces toner in the transition zone, which is between the hopper and the image development zone, into the image development area because of the sweeping motion of the agitator. The weight of the agitator is employed to break up the particles of toner that tend to clump together.
When using a lower melt point toner, the agitator is eventually suspended upon a bed of toner through its repeated actuation by the toner paddle. As a result, the agitator has been found to be ineffective for causing transport of toner particles having a lower melt point. It has been discovered that an external tip load on the farthest reaching portion of the agitator requires 20-50 grams of force on the agitator to return it to its home or rest position when using a lower melt point toner.
This problem is solved through using resilient means such as a spring, for example, to provide an additional tip loading of 20-50 grams on a pivotally mounted agitator. This enables the improved toner cartridge to have a lower melt point toner for increased printing speeds while using particles of relatively smaller size to improve the print quality. Therefore, premature failure to print, which is termed xe2x80x9ctoner starvation,xe2x80x9d is avoided.
A toner cartridge comprises a hopper having an opening for delivering toner out of the hopper, which has a lower wall extending from a bottom of the hopper to a location substantially above the bottom of the hopper to define a bottom of the opening. A paddle is rotatable in the hopper to stir toner such that some toner will move gently toward the opening. The cartridge also has an exit surface to deliver toner from the hopper on the side of the lower wall opposite the hopper with the exit surface sloping downwardly during normal operation of the cartridge. An agitator, which extends across the exit surface, has a first pivot member on one side of the exit surface and a second pivot member on an opposite side of the exit surface. The hopper has support pins for supporting the first pivot member and the second pivot member of the agitator to pivotally support the agitator on the hopper. The agitator is normally located at a home position proximate the exit surface except when moved by the paddle around the first pivot member and the second pivot member. An extension on the agitator extends past the lower wall into the path of the paddle in the hopper when the paddle is rotated. Resilient means mounted on the agitator exerts a force on the agitator to return the agitator to the home position after the agitator is moved from the home position by the paddle engaging the extension during rotation of the paddle and the paddle ceases to engage the extension.